Adsorption Methods

		Activated Alumina Activated alumina is used in packed beds, with longer run times than ion exchange resins, typically several tens of thousands of beds can be treated before arsenic breakthrough. Activated alumina works best in slightly acidic waters (pH 5.5 to 6) – above pH 7 removal efficiency drops sharply. The main factors controlling bed run length are pH and arsenic concentration. Concentrations of other solutes have a relatively small effect. For best results, raw water containing arsenite should be oxidized before treatment. Phosphate, sulfate, chromate and fluoride are also removed by activated alumina, but nitrate is not. Saturated activated alumina can be regenerated with flushing with strong base followed by strong acid. Regenerated media loses some volume and eventually must be replaced. Like ion-exchange resins, activated alumina beds can be clogged by precipitation of iron.
ALCAN household filter
		Ferric Iron Solids Granular ferric hydroxide (AdsorpAs® media) is an effective adsorbent used for the adsorptive removal of arsenate, arsenite and phosphate from natural water. Before the water is passed over the active media, it is aerated for oxidation and prefiltered to remove iron flocs. This method is widely used in community filters (SIDKO filters) in Bangladesh.
SIDKO community filter
		Zero-valent Iron Solids Arsenic can be removed by adsorbtion on a mixture of zero-valent iron filings and sand through formation of coprecipitates, precipitates and adsorption onto ferric hydroxide solids. SONO filters comprise two buckets placed on top of each other, with the top bucket containing sand, iron filings and brick chips and the bottom bucket containing sand, charcoal and brick chips. Problems with this unit may occur if groundwater contains high levels of iron, resulting in clogging of the filter.
SONO household filter

 

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